1. Field of the Invention
The present disclosure relates to wide area network (WAN), and more particularly, to a system and a method for distributing multimedia streaming service request, based on wide area network, which can efficiently support a multimedia streaming service in wide area network.
This work was supported by the IT R&D program of MIC/ITA. [2007-S-016-01, A Development of Cost Effective and Large Scale Global Internet Service Solution]
2. Description of the Related Art
The current network infrastructure has evolved by leaps and bounds, but popularization of World Wide Web, introduction of e-commerce, and activation of online game have exponentially increased demand on network infrastructure, and a network has reached limits in capacity.
FIG. 1 is a block diagram illustrating a basic structure of a conventional multimedia streaming service providing system. Referring to FIG. 1, a system for providing a multimedia streaming service is basically configured with a streaming server for transmitting multimedia contents to a user, a user terminal for showing the transmitted contents to a user, and a network connecting the streaming server to the user terminal.
In such a system, if a bottleneck occurs in the network connecting the user terminal to the streaming server, it is impossible to provide a multimedia streaming service to the user while guaranteeing a desired quality. Accordingly, a contents delivery network (CDN) strategically disposes a plurality of server systems providing the streaming service in various areas, and thus it is used for providing services at positions nearer to users, while guaranteeing quality desired by users.
In the CDN, a wide area server functions as a contents source providing contents to the local servers or local server clusters of each area. Moreover, when a user request a service for specific multimedia streaming contents, the wide area sever receives the service request and redistributes the service request to a local server disposed nearest to the user in terms of geography or a network structure. The local server or the local server cluster provides actual multimedia contents to users. The existing CDN redistributes a service request in a scheme using a domain name server (DNS). This scheme selects a server which is nearest (in terms of geography or the network structure) to a local DNS server managing the DNS queries of users.
However, such a scheme is based on not proximity between a server and an actual client, but proximity between a DNS server having the authority of a server and a client local DNS server. In this case, if a user domain managed by a specific local DNS server is broad, many inaccuracies arise when predicting proximity between a user and an actual server. This scheme has a disadvantage in that two or more local servers or local server clusters are not allowed in a client domain sharing one local DNS server. Moreover, there exist a plurality of intermediate DNS servers between the local DNS servers of clients and DNS servers having the authority of a server, each of the DNS servers caches an address mapping result during time to live (TTL). The TTL value may be adjusted. However, since the very small TTL value increases the load of the DNS servers and the address mapping requests over a network, network providers do not favor a very small TTL value. Therefore, in most cases, the network providers ignore a certain limits value or less TTL values. In view of these, a request distributing scheme based on the DNS does never have a control right, and thus it causes an unsuitable request distribution result when changing a network state.
A wide area request distributing scheme for the CDN selects a local server capable of providing services to a user at the highest quality and the lowest cost possible upon the user's request, and thereafter must distribute the request to the corresponding local server. Generally, a local server that is nearest to a user in terms of geography or network is selected as a local server to provide the service. The network proximity measurement scheme uses a static scheme predicting proximity in view of network topology such as network hop counts, or a dynamic scheme measuring round trip time (RTT) or available bandwidth. In a case of the static scheme, since a proximity information is fixed, the static scheme has a high performance for the selection of local servers whereas does not reflect the real-time environment of the network. On the other hand, the dynamic scheme may reflect the real-time environment of the network to perform an exact selection, but delays the execution of services because of taking much time in predicting proximity. Moreover, when a corresponding local server is down, existing local server selection schemes prevent a service request from being distributed to the corresponding local server. However, since the existing local server selection schemes check only whether the local server is alive, they do not prevent a service request from being distributed to a corresponding local server which cannot actually execute services by exceeding its service capacity.